The present invention relates to two-cycle internal combustion engines and, more particularly, to a method and apparatus for increasing horsepower without increasing RPM in a two-cycle engine.
Conventional two-cycle engine blocks used for medium to high power applications such as jet skis are cast blocks. Such engines typically produce about 50 HP at 6500 RPM. Horsepower drops down as engine speed decreases. For applications such as jet skis, it is desirable to be able to produce higher horsepower at lower engine speed but, at the same time, it is imperative that the engine be small and lightweight. While cast engines meet the small and lightweight criteria, efforts to increase horsepower often result in cracking or damage and failure of the cast block from the added stress. It is believed that such failures in cast blocks stem from the inherent difficulty in obtaining defect free castings, i.e., minute voids or imperfect grain structure are common in engine size castings.
In addition to the disadvantages of cast blocks, it has also been found that efforts to increase power output often result in "blown" head gaskets, i.e., pressure loss through leakage between the cylinder block and cylinder head. It is common in such small block engines to form the block and head from aluminum alloy. Under high temperature and stress, it is believed that the head can warp or deform thus allowing leakage between the head and block.
Still another disadvantage of the prior art cast engine blocks is in the shape and configuration of each cylinder and its associated fuel transfer passages and exhaust passages. Conventionally, the designs are optimized for ease of manufacture and the general design of such small cylinder blocks has not been changed significantly since the inception of two-cycle engines. However, such designs are not believed optimal for engine performance.